In constructing a frame of a building by assembling column members and beam members which are made of structural steel or precast concrete at a work site, a method shown in FIG. 17 is generally employed. In this conventional method, the process for constructing the frame of the building is progressed by lifting up the column members and the beam members with the use of a lifting crane placed on the circumferences of the building to be erected or on the constructed beams or slabs for the building. Such column members and beam members are assembled and combined under the condition having no work scaffolds.
In this conventional method, for example, an arm derrick type tower crane, an arm horizontal type tower crane or the like, as shown in FIG. 17, are used for lifting the beam and column members. The cranes to be used in a construction site are difficult to change positions once they are fixed on the frame of the building or on the ground, and thus, it is preferable in the conventional process to utilize relatively large cranes which can lift the column and beam members to the position higher than the top of the building to be built so that these cranes can be used until the final stage of the construction of the building without changing the positions. Further, for the sake of workability and efficiency, the numbers of cranes to be used in the construction area are limited to a certain small numbers. In such cases, again, cranes with larger lifting radii are commonly used so as to reach to the end of the building. As a result, as shown in FIG. 17, the crane 19 is scaled up and becomes heavier, which requires that the columns C and beams B of the building to be built have to be reinforced by placing braces 18 within the frames in order to support the load of the cranes. If such cranes are attached on the ground of the construction site, the special foundation for the cranes on the ground becomes necessary to fully support the weight of the cranes. Therefore, the conventional method for assembling a frame inherently results in considerable cost increase.
In addition, in the conventional methods, scaffolds cannot be provided to the columns and the beams until the assembly of frames is completed. The scaffold is a temporary platform used by workers in the construction of a building. Thus, the assembling work in the conventional method has to be practiced in the condition having no scaffolds. Therefore, the construction workers have to practice under the very dangerous condition where they directly climb the columns and walk on the beams, resulting in the serious shortage of workers.
Furthermore, since a roof or a cover cannot be placed during the constructing process of frames in the conventional method, the assembly work has to be done on the wet steel structure, for example, in case of rain, which further increases danger in the working condition. Due to such serious increase of danger, the works under the rainy weather has to be stopped or postponed.